In the classic view of spinal cord neurophysiology, the thousands of synaptic inputs that impinge on motor neurons are integrated and converted to action potentials. In recent years, however, it has become evident that he dendrites of motor neurons do not act as passive recipients of synaptic input; they contain voltage-sensitive onductances that are influenced by neuromodulatory input from monoaminergic axons originating in the brainstem: At high levels of monoaminergic input, the persistent inward currents that are generated in the dendrites become so large that the discharge rates required for maximal activation of muscle fibers can be achieved with relatively minor amounts of synaptic input. Thus, active dendritic currents rather than ionotropic synaptic currents may dominate integration by motor neurons during normal motor behavior. One consequence of this possibility is that it becomes difficult to infer patterns of synaptic input from recordings of motor unit activity made in human subjects and patients. The purpose of this R13 application is to request support for a 3-day meeting that will provide a forum for the exchange of information between investigators who study motor neuron properties in experimental animals and those who record motor unit activity in humans. The meeting, which is titled "'Active Dendrites in Motor Neurons: Mechanisms and Effects on Motor Output", will be held at the University of Colorado at Boulder on June 24-26, 2004. The meeting will involve about 75 participants: 26 invited speakers, approximately 30 trainees (graduate students and postdoctoral fellows), and a number of collaborators. The invited speakers, all of whom have agreed to participate in the meeting, are PIs who direct research programs that study either motor neuron properties in experimental animals or motor unit activity in humans. Nine of the 26 invited speakers are women. The meeting format will consist of podium presentations (30, 10, and 2 rain), poster sessions, and significant time for discussion. The meeting will also include three young investigator awards to encourage participation by trainees in the meeting. The abstracts submitted by each invited speaker will be posted on a publicized website. Our expectation is that the meeting will provide an opportunity to review current knowledge on motor neuron properties and motor unit behavior, to identify critical gaps in existing knowledge, and to formulate a research agenda that can address these issues.